This invention pertains to an encoding method for, as well as a transcoding method and apparatus for transcoding the bit rate of, an encoded video stream encoded with some encoding method.
Through the swift growth of moving image processing technology in recent years, objects/devices handling moving images have come to be wide-ranging. Further, since the data volume of moving images generally becomes very large, it is common to make the data available after performing compressive encoding in the case of handling moving images as digital data.
Conventionally, compressive encoding is used which corresponds to the objective of use and the targeted device, and there is carried out transcoding in converting moving image data compressively encoded with some encoding method to data having a different encoding method, with the objective of sharing data between different devices. Moreover, without changing the compressive encoding method, operations like modifying the size and the frame rate of the moving images and increasing the compression ratio are carried out to make the bit rate suitable to the use.
For conversions like these, a method is adopted in which, after temporarily decoding bit stream of the transcoding source, it is recoded with the desired encoding format, but for the purpose of reducing the transcoding processing load on that occasion, techniques of performing recoding using intermediate information during transcoding are proposed in JP-A-2003-264840, JP-A-2003-116104, JP-A-2003-61089, JP-A-2002-320228, and JP-A-2001-268578.
However, since, in transcoding with the aforementioned conventional technology, the first frame is decoded and the intermediate information obtained on the occasion of this first decoding is directly used for the encoding of the first frame, it has not been possible to use the intermediate information of the not yet decoded second and third frames for the encoding of the first frame.